Three million tons of old lead line the walls and fixtures of 57 million American homes. Three to four million young children from all levels of society are exposed to environmental sources of lead at concentrations that place them at risk of adverse health effects. Several hundred thousand of them have absorbed enough lead to significantly slow their minds and alter their behavior. Yet, there is no tool available for measuring total pediatric body burden of lead. This proposal describes the development of an x-ray fluorescence (XRF) instrument that will allow measurement of body lead burden in children in vivo and noninvasively. Experience gained from the development of an adult XRF instrument, during a previous grant serves as our stepping stone. This proposal describes the development of a multi- detector and count rate limited XRF system to improve detection sensitivity to the 2.5 ppm level in a 10-minute measurement period. The program will include the design and packing of a multi-detector configuration, and improvement in source-collimator coupling to increase source irradiation, thus matching the count rate improvement. This will be achieved with the same source intensity used in the adult XRF device. The ultimate machine will provide a unique capability as: (1) a diagnostic tool in determining the presence of bone lead levels; (2) a mass screening device for indication of chronic low level lead exposure; and (3) a monitoring device in following progress during chelation therapy.